Within various fields of electronics, a need for protecting electronic equipment against over-voltage may arise. Over-voltage refers herein to when electronic equipment is exposed to voltages that are high enough to harm the electronic equipment. Therefore, electronic circuits for protecting a piece of electronic equipment against over-voltage have been developed. An electronic circuit of the abovementioned kind is herein referred to as an over-voltage circuit. Thanks to the over-voltage circuits, the piece of electronic equipment does not become exposed to over-voltages. Thus, the piece of electronic equipment does not break or become damaged. A breakage or damage of the piece of electronic equipment may disadvantageously lead to an interruption in any activity requiring the piece of electronic equipment to be fully functional.
In FIG. 1, a known over-voltage circuit 10 for protecting a device 11 against over-voltage is shown. The device may be any kind of electronic equipment. The over-voltage circuit 10 comprises an input connector 12, an output connector 13, a Zener-diode 14 and a resistor 15. The input connector 12 is arranged to receive an input voltage Vin, which sometimes may be high enough to damage or even break the device 11. Hence, an over-voltage may be feed into the input connector 12 at any time. The output connector 13 is arranged to feed voltage to the device 11. As can be seen from the Figure, the Zener-diode 14, in reversed-bias, and the resistor 15 are arranged such as to prevent a harmful over-voltage to be applied over the device 11. The device 11 is protected from over-voltage thanks to that the voltage over the Zener-diode 14 is close to or at the so called breakdown voltage of the Zener-diode 14 for a wide range of currents. Clearly, the voltage over the Zener-diode 14 is the same as the voltage over the device 11. The wide range of current may originate from current that may flow though the Zener-diode 14 due to over-voltage at the input connector 12. It shall be understood that the device 11 is required to endure, without damage, voltages up to the breakdown voltage of the Zener-diode 14.
In some fields of electronic circuit, it may be a disadvantage to use resistors and Zener-diodes as in the example above. It may for example be undesirable that the Zener-diode and the resistor occupy valuable space on a circuit board of the electronic circuit. This may lead to that the circuit broad must be larger or that other components must be removed or re-arranged. Sometimes, it may be that the Zener-diode and the resistor are unnecessarily costly in terms of purchase price. Additionally, some power is dissipated over the resistor 15, which in applications requiring low power consumption is a further disadvantage.